Fluororubber is drawing attention as a material for fuel hoses, etc., for its excellent heat resistance, oil resistance, ozone resistance, chemical resistance, etc., but it is expensive. Accordingly, a laminate structure of fluororubber and epichlorohydrin rubber is used to retain oil resistance as well as flexibility, while reducing the usage of fluororubber, with the fluororubber placed on the side contacting the oil medium.
However, fluorine is a material with low surface energy that does not bond easily with other polymers, and therefore an additive must be compounded to epichlorohydrin rubber to improve adhesiveness. For this additive, 1,8-diazabicyclo (5,4,0) undecene-7 salt (Patent Literatures 1 and 2), polyether compound whose number-averaged molecular weight is 1000 or more (Patent Literature 3), strongly basic compound having an amidine skeleton in its molecule, combined with epoxy resin (Patent Literature 4), and 1,8-diazabicyclo (5,4,0) undecene-7 salt, etc., combined with magnesium oxide, silica, epoxy resin (Patent Literature 5), have been proposed. Epichlorohydrin rubber compounded with any such additive can be vulcanization-bonded directly to fluororubber; however, the scorching time becomes shorter and burning occurs easily during kneading, storage, and molding, and the workability drops as a result. In other words, adhesiveness and workability are two properties that are difficult to achieve at the same time, when it comes to rubber compositions.
In Patent Literature 6, adding 1,8-diazabicyclo (5,4,0) undecene-7, etc., epoxy resin, water-supporting substance to improve adhesiveness, and further compounding N-cyclohexyl thio phthalimide and/or nickel dibutyl dithio carbamate as an anti-scorching agent is proposed. However, since the epoxy resin starts polymerizing with the 1,8-diazabicyclo (5,4,0) undecene-7, etc., which is a strong base, functioning as a curing accelerator, a satisfactory scorching time cannot be achieved even though an anti-scorching agent has been compounded.
On the other hand, various methods have been attempted to improve adhesiveness by treating the surface of a fluorine member, and a method of vulcanization-bonding a fluororesin layer whose surface has been plasma-treated, with epichlorohydrin rubber, has been proposed (Patent Literature 7).
Additionally, Patent Literature 8 permits vulcanization-bonding of NBR or other synthetic rubber with fluororubber using an additive that does not cause scorching easily. This additive can be used in epichlorohydrin rubber so that it can be vulcanization-bonded with fluororubber; however, high levels of adhesiveness and workability cannot be achieved at the same time.